Dual band lens system incorporating molded chalcogenide

Abstract

An image forming system and lens system including at least one molded chalcogenide lens element and configured to simultaneously image light at the medium wave infrared region (MWIR) and the long wave infrared region (LWIR) at a common focal plane.

1. A lens system comprising:
 an objective lens unit configured to establish an aperture stop; 
 a positive triplet configured to simultaneously image light at an aperture stop in a wavelength range from about 3 to about 5 micrometers and light in a wavelength range from about 8 to about 12 micrometers to a common focal plane, said positive triplet comprising a first molded aspheric chalcogenide lens element positioned to receive light directly from said aperture stop and having an associated Abbe number V 3-13  in the range from about 47.799 to 47.837 calculated as:
     V   3-13 =(N 8−1 )/(N 3− N 13 ) 
 
 
     where N 8  is the refractive index at a wavelength of 8 micrometers, N 3  is the refractive index at a wavelength of 3 micrometers and N 13  is the refractive index at a wavelength of 13 micrometers. 
   
   
     2. The lens system of  claim 1 , wherein said frist molded chalcogenide lens element has an index of refraction in the range from about 2.5009 to 2.5021 at 8 micrometers. 
   
   
     3. The lens system of  claim 1 , said objective lens unit comprising a second molded aspheric chalcogenide lens element. 
   
   
     4. The lens system of  claim 3 , wherein said objective lens unit further comprises a negative germanium lens element and a negative zinc sulfide lens element. 
   
   
     5. The lens system of  claim 4  wherein said positive triplet further comprises a germanium lens element and a zinc sulfide lens element. 
   
   
     6. A system compnsing:
 an objective lens unit configured to establish an aperture stop; 
 a positive triplet configured to simultaneously image light at an aperture stop in a wavelength range from about 3 to about 5 micrometers and light in a wavelength range from about 8 to about 12 micrometers to a common focal plane, said positive triplet comprising a first molded aspheric chalcogenide lens element positioned to receive light directly from said aperture stop and having an associated Abbe number V 3-13  in the range from about 47.799 to 47.837 calculated as:
     V   3-13 =(N 8−1 )/(N 3− N 13 ) 
 
 
     where N 8  is the refractive index at a wavelength of 8 micrometers, N 3  is the refractive index at a wavelength of 3 micrometers and N 13  is the refractive index at a wavelength of 13 micrometers,
 a detector positioned at said common focal plane and configured to create electrical impulses in response to said light in said wavelength range from about 3 to about 5 micrometers and said light in said wavelength range from about 8 to about 12 micrometers; and 
 a signal processing unit configured to process said electrical impulses for displaying an image. 
 
   
   
     7. The system of  claim 6 , wherein said first molded chalcogenide lens element has an index of refraction in the range from about 2.5009 to 2.5021 at 8 micrometers. 
   
   
     8. The system of  claim 6 , said objective lens unit comprising a second molded aspheric chalcogenide lens element. 
   
   
     9. The system of  claim 8 , wherein said objective lens unit further comprises a negative germanium lens element and a negative zinc sulfide lens element. 
   
   
     10. The system of  claim 9 , wherein said positive triplet further comprises a germanium lens element and a zinc sulfide lens element. 
   
   
     11. A method comprising:
 imaging light in a wavelength range from about 3 to about 5 micrometers and light in a wavelength range from about 8 to about 12 micrometers at an aperture stop established by an objective lens unit to a common focal plane using a positive triplet comprising a first molded aspheric chalcogenide lens element positioned to receive light directly from said aperture stop and having an associated Abbe number V 3-13  in the range from about 47.799 to 47.837 calculated as:
     V   3-13 =(N 8−1 )/(N 3− N 13 ) 
 
 
     where N 8  is the refractive index at a wavelength of 8 micrometers, N 3  is the refractive index at a wavelength of 3 micrometers and N 13  is the refractive index at a wavelength of 13 micrometers; and
 displaying an image in response to said light at said common focal plane. 
 
   
   
     12. The method of  claim 11 , said objective lens unit comprising a second molded aspheric chalcogenide lens element. 
   
   
     13. The method of  claim 12 , wherein said objective lens unit further comprises a negative germanium lens element and a negative zinc sulfide lens element. 
   
   
     14. The method of  claim 13 , wherein said positive triplet further comprises a germanium lens element and a zinc sulfide lens element.